This species is very small, a mature adult growing to only 3-3.5 in (7.6-8.9 cm) in length. The male Costa&#39;s has a mainly green back and flanks, a small black tail and wings, and patches of white below their gorgeted throat and tail. Its most distinguishing feature is its vibrant purple cap and throat with the throat feathers flaring out and back behind its head. The female Costa&#39;s hummingbird is not as distinct as the male, having grayish-green above with a white underbelly.